This invention relates to fluid filters, and more particularly to a self-cleaning filter which automatically flushes filtered matter from the filter element each time line pressure to the filter housing is shut off.
Conventional filters for filtering solid particles from oil or water, for example, for the most part comprise a filter housing having an inlet opening on one side of the filter element, and an outlet opening on the other side of the filter element. Unfiltered fluid is forced through the filter element under pressure, and filtered matter accumulates, usually as a sediment, in a housing. A drain valve can be opened to remove the trapped sediment from the housing.
The filter elements of such filters often become clogged from the filtered matter trapped by the element. Often the efficiency of the filter is reduced appreciably after a relatively short filtering time. Many filters, such as cartridge type oil filters, solve the clogging problem by providing removable filter elements. However, it can be time-consuming and costly to constantly change filter elements in many filtering operations.
U.S. Pat. Nos. 515,769 to Harris, 3,445,002 to Muller and 3,617,551 to Johnston et al. disclose filters having compressible filter elements which can be priodically squeezed to flush filtered matter from the element. In one instance, the compressible filter element is flushed by manually squeezing it each time it is desired to clean the element. In another instance line pressure is reversed, when desired, to compress the to filter element to backflush filtered matter from it. These methods of periodically cleaning the filter element avoid frequent changing of the filter element. However, in the time intervals between cleaning of the filter element, filtered matter trapped in the filter element can appreciably reduce filtering efficiency. This is especially true in microfiltration applications involving filters having micron size pores which can be rapidly clogged during use. Moreover, it can be an annoyance to require either frequent manual cleaning of the filter element or frequent adjusting of valves to backflush the filter.
The present invention provides a self-cleaning filter in which the filter element is automatically cleaned each time line pressure is shut off. Thus, in applications involving constant stopping and starting of filtering operations, the filter element remains substantially free of trapped particles. As a result, filtering efficiency is improved and filtering operations can proceed without requiring frequent changing of the filter element, manual cleaning of the filter, or reversing of line flow. The filter of this invention also allows the filter element to provide a practical means of water purification in that the pores of the filter element can be of micron size and still operate efficiently because of its ability to remain clean during filtering operations.